alknet/docs/architecture/crates/call/README.md

---
status: draft
last_updated: 2026-06-26
review: call/review-call passed 2026-06-23 — registry, protocol, ADR (005/012/014/015/016/017/022/023/024), security, and pattern-consistency checks all conformant; 159 unit/integration tests green; `cargo build`, `cargo clippy -- -D warnings`, `cargo fmt --check`, `cargo test` clean. Call-completion gap (ADR-017 client/adapter surface) addressed 2026-06-26 — ADR-028 + client-and-adapters.md added; implementation pending.
---

# alknet-call

Structured RPC over QUIC: operations, request/response, streaming subscriptions, and service discovery. Implements `ProtocolHandler` on ALPN `alknet/call`.

## Documents

| Document | Status | Description |
|----------|--------|-------------|
| [call-protocol.md](call-protocol.md) | draft | CallAdapter, EventEnvelope framing, stream model, PendingRequestMap, bidirectional calls |
| [operation-registry.md](operation-registry.md) | draft | OperationSpec, Handler, OperationRegistry, AccessControl, service discovery, irpc integration |
| [client-and-adapters.md](client-and-adapters.md) | draft | CallClient (outbound connection opener), from_call / from_jsonschema, OperationAdapter trait, adapter location map, no-env-vars invariant, exchange-of-operations pattern |

## Applicable ADRs

| ADR | Title | Relevance |
|-----|-------|-----------|
| [001](../../decisions/001-alpn-protocol-dispatch.md) | ALPN-Based Protocol Dispatch | CallAdapter registers on ALPN `alknet/call` |
| [002](../../decisions/002-protocol-handler-trait.md) | ProtocolHandler Trait | CallAdapter implements ProtocolHandler |
| [003](../../decisions/003-crate-decomposition.md) | Crate Decomposition | alknet-call depends on alknet-core and irpc |
| [013](../../decisions/013-rust-canonical-implementation.md) | Rust as Canonical Implementation Language | Adapter traits defined in Rust; TS is reference/browser adaptation |
| [004](../../decisions/004-auth-as-shared-core.md) | Auth as Shared Core | AuthContext passed to call handlers |
| [005](../../decisions/005-irpc-as-call-protocol-foundation.md) | irpc as Call Protocol Foundation | irpc provides framing and service dispatch |
| [006](../../decisions/006-alpn-convention-and-connection-model.md) | ALPN String Convention | `alknet/call` ALPN, one ALPN per connection |
| [007](../../decisions/007-bistream-type-definition.md) | BiStream Type Definition | CallAdapter receives Connection, not BiStream |
| [008](../../decisions/008-secret-service-integration.md) | Vault Integration Point | Vault accessed at assembly layer, not on the wire |
| [010](../../decisions/010-alpn-router-and-endpoint.md) | ALPN Router and Endpoint | Static handler registration |
| [012](../../decisions/012-call-protocol-stream-model.md) | Call Protocol Stream Model | Bidirectional streams, EventEnvelope, ID-based correlation |
| [014](../../decisions/014-secret-material-flow-and-capability-injection.md) | Secret Material Flow and Capability Injection | Call protocol carries no secret material; capabilities injected at assembly layer |
| [015](../../decisions/015-privilege-model-and-authority-context.md) | Privilege Model and Authority Context | `internal` = authority switch not ACL skip; External/Internal visibility; handler identity + scoped env |
| [016](../../decisions/016-abort-cascade-for-nested-calls.md) | Abort Cascade for Nested Calls | `call.aborted` cascades to descendants; default `abort-dependents`, `continue-running` opt-in |
| [017](../../decisions/017-call-protocol-client-and-adapter-contract.md) | Call Protocol Client and Adapter Contract | `CallClient` opens connections; `from_call` imports remote ops; connection direction independent of call direction |
| [022](../../decisions/022-handler-registration-provenance-and-composition-authority.md) | Handler Registration, Provenance, and Composition Authority | Registration bundle carries provenance, composition authority, scoped env, capabilities |
| [023](../../decisions/023-operation-error-schemas.md) | Operation Error Schemas | Operations declare domain errors; `call.error` carries typed `details`; adapter fidelity |
| [024](../../decisions/024-operation-registry-layering.md) | Operation Registry Layering | Curated (static) + session/connection overlays (dynamic); `OperationEnv` as trait-object integration point; `OperationContext.env` split into `scoped_env` (data) and `env` (dispatch trait) |
| [028](../../decisions/028-callclient-peer-scoped-registry-filtering.md) | Peer-Scoped Registry Filtering for CallClient Inbound Dispatch | Default-deny peer-scoped registry view; `remote_safe` marking on `HandlerRegistration`; trusted-peer opt-in; locks the ADR-017 §1 security-dimension one-way door |

## Relevant Open Questions

| OQ | Title | Status | Relevance |
|----|-------|--------|-----------|
| OQ-07 | Call protocol scope within a connection | resolved (ADR-012) | Stream model, multiplexing, scope |
| OQ-13 | Operation path format and routing scope | resolved | `/{service}/{op}` is the correct design; remote dispatch is a separate layer |
| OQ-14 | Batch operation semantics | resolved | Correlated `call.requested` events is the correct protocol design |
| OQ-16 | Safe vault operations for call protocol exposure | resolved (ADR-014) | None exposed for now |
| OQ-19 | Session-scoped operation registries | resolved | Agent-written operations overlaid on curated registry via `OperationEnv` trait layering. Protocol doesn't need changes; `OperationEnv` must remain a trait. Generalized by ADR-024 to cover connection-scoped overlays. |
| OQ-25 | Remote-safe marking shape for CallClient peer-scoped filtering | open (two-way) | Existence of default-deny filtering locked by ADR-028; shape (`remote_safe: bool` v1 vs per-peer allowlist) is the two-way-door remainder |
| OQ-26 | OperationAdapter error type (AdapterError variants) | open (two-way) | `import()` returns `Result<_, AdapterError>`; variants decided in implementation |
| OQ-27 | from_call re-import trigger | open (two-way) | v1 default: auto-on-reconnect; explicit `refresh()` is additive |
| OQ-28 | from_call namespace collision behavior | open (two-way) | v1 default: error on collision (no prefix by default) |
| OQ-29 | CallClient TLS client-auth and remote-identity verification | open (two-way) | v1 connects with `with_no_client_auth()` + `AcceptAnyServerCertVerifier`; wiring RawKey client-auth and a real `ServerCertVerifier` is additive (no-env-vars invariant unaffected — `auth_token` flows via call-protocol payload, not TLS) |

## Key Design Principles

1. **One connection, full access**: An `alknet/call` connection gives access to the entire operation registry — calls, subscriptions, batch, schema.
2. **Protocol is symmetric**: Both sides can initiate calls. The server calling a client uses the same EventEnvelope format and correlation.
3. **Stream-agnostic correlation**: PendingRequestMap correlates by request ID, not by stream. The protocol works with any stream arrangement.
4. **Operation registry is layered**: The curated layer (`Local` provenance) is static — registered at startup by the CLI binary, immutable for the process lifetime. Session (`Session`) and imported (`FromCall` etc.) ops are dynamic overlays at their respective scopes (per-session, per-connection). The registry supports JSON Schema discovery. See ADR-024.
5. **irpc is one dispatch backend**: Local operations dispatch directly. irpc service calls (in-process, type-safe) are internal. The call protocol is the external interface.
6. **Local dispatch only**: The operation registry dispatches to local handlers. Remote dispatch (federation, head/worker routing) would be a separate mechanism at a different layer, not a modification to alknet-call's path format.
7. **No secret material on the wire**: The call protocol carries no private keys, API keys, mnemonics, or decrypted credentials. Handlers receive outbound credentials through `OperationContext.capabilities`, injected at the assembly layer. See ADR-014.
8. **Abort cascades to descendants**: `call.aborted` for a parent request cascades to all non-terminal descendants. Default `abort-dependents`; `continue-running` opt-in. See ADR-016.
9. **Internal calls switch authority context, not skip ACL**: The `internal` flag marks composition-originated calls. ACL runs against the handler's composition authority, not the caller's and not as a blanket skip. Operations have External/Internal visibility. Scoped composition env bounds reachability. See ADR-015, ADR-022.
10. **Provenance determines composition capability**: Only `Local` and `Session` ops can compose. Leaves (`FromOpenAPI`, `FromMCP`, `FromCall`) are forwarding stubs — they don't get composition authority or a scoped env. The assembly layer is the sole grantor of composition authority. See ADR-022.
11. **Connection direction is independent of call direction**: Who opens the QUIC connection is a connection-layer concern, not a protocol-layer concern. Both sides can call each other once connected. The `CallAdapter` accepts connections; the `CallClient` opens them; both produce the same `CallConnection` and dispatch through the same loop. See ADR-017, [client-and-adapters.md](client-and-adapters.md).
12. **CallClient registry is default-deny**: A `CallClient` exposes no operations to the remote peer unless explicitly marked remote-safe. Sharing the global registry is an explicit trusted-peer opt-in, never the default. This prevents a remote peer's call from triggering dispatch that populates `OperationContext.capabilities` from the local node's registration bundle. See ADR-028.
13. **Adapter trait lives with the types; implementations live with their transport**: `OperationAdapter` is in `alknet-call`; `from_call`/`from_jsonschema` are in `alknet-call` (QUIC / pure parse); `from_openapi`/`from_mcp`/`to_openapi`/`to_mcp` are in `alknet-http` (reqwest / axum). `alknet-call` stays lean — no HTTP client, no HTTP server. See [client-and-adapters.md](client-and-adapters.md).
14. **No handler reads outbound credentials from any source other than `OperationContext.capabilities`** (no-env-vars invariant): the credential injection path is vault → assembly layer → `Capabilities` → `HandlerRegistration.capabilities` → `OperationContext.capabilities` → handler. Downstream consumers' `std::env::var` reads are unreachable because the assembly layer never calls `Default::default()`. See ADR-014, [client-and-adapters.md](client-and-adapters.md).